The present invention relates to an earth-working machine such as an excavator for digging ditches in road construction, and more particularly to an earth-working machine having a turntable and a carriage which are driven by respective hydraulic motors so as to be controllably angularly movable independently on a self-propelled mobile chassis for enabling an excavating mechanism on the carriage to turn in various angular ranges for avoiding interference with surrounding traffic and/or objects and providing wide working areas for the excavating mechanism.
Conventional earth-working machines or excavators include an excavating mechanism composed of a boom or bucket arm having a bucket on its distal end for trenching a ditch in a road. In operation, the material scooped by the bucket is transferred back by turning the boom around the machine. Since the boom is angularly moved through an semicircular angule range, the boom and the bucket as they move project laterally of the machine, resulting in the danger of interfering with surrounding traffic and/or objects. Therefore, a large working radius or range clear of any obstructions should be reserved around the machine for allowing safe swinging movement of the boom. This requirement however is difficult or even impossible to meet in situations where only relativey small or limited spaces are available for the machine.
To eliminate such a difficulty, there has been proposed an excavator having a turntable rotatably mounted on a mobile chassis and a carriage rotatably mounted on the turntable and supporting an excavating mechanism, the turntable and the carriage having shafts positioned out of coaxial relation. With this arrangement, the bucket on the boom is allowed to move over the chassis without appreciably projecting laterally thereof when the turntable and the carriage are turned about their shafts. Therefore, unwanted interference with traffic or objects is prevented around the machine, and the excavator can be placed in relatively small spaces for road construction or other earth-moving applications. The proposed excavator are however less resistant to vibrations and susceptible to adverse environments. Another problem is that the turntable and the chassis which are driven by respective hydraulic motors tend to be brought out of synchronism when they are operated for a long time. Therefore, it has been necessary to correct the relative angular positions of the turntable and the chassis by independently operating the hydraulic motors. Such angular positional adjustments have heretofore been carried out by a manual operation, which is time-consuming, troublesome, and not reliable sufficiently.